This preclinical research program, using mice as the experimental animals, is designed to: 1. Define the severity and time course of cancer treatment (chemotherapy and/or radiotherapy) induced changes in a number of nutrition-related factors, such as: animal weight, food and water intake, rate of gastric emptying, and intestinal transit time. 2. Assess the extent to which the above factors contribute to the severity of acute gastrointestinal tissue toxicity as manifest by a reduction in the proliferative rate of the epithelial lining. These studies will be accomplished by simulating treatment-induced nutritional changes with restricted diets and examining gastrointestinal cell proliferation produced by the dietary change alone. 3. Attempt to ameliorate treatment associated gastrointestinal toxicity through nutritional modification, such as enteral nutrient administration and treatment dose-time scheduling. 4. Assess the effect of pretreatment nutritional status on the proliferative response of the gastrointestinal epithelium to therapy. Diet modification will range from complete fasting, through changes in caloric, bulk, protein and fat content.